1. Field of the Invention
The present invention relates to a rotatable about an axis of symmetry, ultrasonic annular core bit provided with cutting or abrasive bodies for abrasive cutting mineral components formed, e.g., of stone and having axial ultrasonic excitation.
2. Description of the Prior Art
Usually, a pot-shaped, annular core bit includes a cylindrical tube provided with abrasive bodies at its end side, and a cover provided at the opposite end side of the cylindrical tube and secured thereto and having, in its center, a shank to be received in a rotary power tool. Upon a conventional superimposition of ultrasound in the range from 20 kHz to 200 kHz at the natural frequency of the core bit, the bit will be excited in its center by an actor in the shank provided in the cover. Such core bits can be only realized with cylindrical tubes having only a small diameter up to 100 mm. This is because upon engaging the to-be-cut component, with a larger diameter of the tube, i.e., with a large ratio of the tube diameter to the excitation diameter of the actor, no robust axial longitudinal oscillations are excited, in particular, with high damping imparted to the cylindrical tube by axial forces necessary for effecting an abrasive cutting.
German Publication DE-3812917 discloses a slot borer driver with not a specified, natural frequency and having a plurality of elongate offerings formed in the annular crown.
German Publication DE-3635806 discloses a tool with a regulated ultrasonic vibrator and provided with a plurality of equidistant elongate slots in a cylindrical base body, with the webs acting as pure longitudinal oscillators.
German Publication DE-4444853 discloses an annular core bit having a cylindrical tube with a cover in the center of which a natural frequency is applied to provide for axial flexural oscillation. At that, a grinding disc, which is subjected to the flexural oscillations and has a thickness that deviates from abrasive bodies, has a concentric projection in a geometrically nondefined location.
German Publication DE-19758243 discloses an ultrasonic transducer for increasing a directive efficiency of a flat, flexurally oscillating plate subjected to the action of a sound field and having, in its center, a projection provided on the nodal circle of amplitude oscillations.
An object of the present invention is to provide an annular core bit having a large diameter and characterized at a central, axial ultrasonic excitation, by a robust excitation behavior for exciting axial longitudinal oscillations in the cylindrical tube.
Another object of the present invention is to provide an annular bit with an increased axial oscillation amplitude at the axial end of the cylindrical tube.